#validates_attachment_content_type(*attr_names) ⇒ Object

Places ActiveModel validations on the content type of the file assigned.
The possible options are:

content_type: Allowed content types. Can be a single content
type or an array. Each type can be a String or a Regexp. It should be
noted that Internet Explorer uploads files with content_types that you may
not expect. For example, JPEG images are given image/pjpeg and PNGs are
image/x-png, so keep that in mind when determining how you match. Allows
all by default.

not: Forbidden content types.

message: The message to display when the uploaded file has an
invalid content type.

if: A lambda or name of an instance method. Validation will
only be run is this lambda or method returns true.

unless: Same as if but validates if lambda or
method returns false.

NOTE: If you do not specify an [attachment]_content_type field on your
model, content_type validation will work _ONLY upon assignment_ and
re-validation after the instance has been reloaded will always succeed.
You'll still need to have a virtual attribute (created by
attr_accessor) name [attachment]_content_type to be able to
use this validator.